Human use of cathinones for their psychoactive properties traces back to prehistory. Known as “khat” by the people of eastern Africa, the leaves and twigs of the Catha edulis shrub have been chewed for centuries in traditional cultures.

The effects could be described as somewhere between a serious coffee habit and mild amphetamine use. This is unsurprising to chemists, because the cathinone and amphetamine molecules are almost identical (there’s just one little difference: a “beta-ketone”). Although not entirely free of negative consequences, traditionally managed khat chewing has a relatively mild impact on most users.

Mephedrone (AKA “4-methylmethcathinone”), however, is not normal cathinone: it’s a “substituted cathinone”. That means it’s a molecule with the same backbone as the basic cathinone, but with some extra bits stuck on the ends.

In a similar way, MDMA (“ecstasy”) is a substituted amphetamine. Just as the effects of an ecstasy pill are very different from those of straight amphetamines, the impact of mephedrone is quite different from traditional khat.

Mephedrone users enjoy euphoria, mental and physical stimulation, an enhanced sense of touch and empathy and a bit of sensory distortion. They also frequently enjoy a strong craving for more of the drug.

Mephedrone developed a following among recreational drug users in the late 2000s, beginning in Europe but now spreading worldwide. Among drug-using clubbers in the UK, mephedrone is as popular as ecstasy or cocaine. Although scientific knowledge of mephedrone was essentially zero when this all began, over the last year we’ve made a start on figuring out what’s going on.

One team of researchers used high-precision drilling and some very fine needles to sample the brain chemistry of rats that were high on mephedrone. They found the drug caused a fast and vigorous release of neurotransmitters into parts of the brain strongly involved in craving and addiction.

Another team took brains from rats and mixed it with special radioactive stuff designed to latch on to the same bits they guessed might be affected by mephedrone. As they thought, less of the radioactive stuff stuck onto the mephedrone-treated tissue, showing that the drug had attached itself in those places.

These were the locations of “transporters”, neural structures that pick up and recycle neurotransmitters after they’ve done their thing. Clogging up these transporters can make neurotransmitters hang around for longer than they should, which increases the effect they have on the brain.

A third team (of which I was a part) used a method involving proteins and antibodies to hijack a rat’s immune system.

We do this to trick the immune response into changing the colour of neurons that have been working hard in the recent past, so we can later look and see which ones were marked.

By doing this, you get what’s essentially a timelapse version of a brain scan: for example, it can tell you what neurons are strongly activated by a particular drug.

When you compare the mephedrone “scan” with what you’d see with ecstasy or methamphetamine, the areas strongly activated by mephedrone are a close match for a combination of those found with the other two drugs.

This matches up with what people had been telling us about the experience of taking the drug, and it suggests there should be some common features between how these three drugs (mephedrone, ecstasy and methamphetamine) go about their business.

But enough about how it works: can it kill you?

Well, yes. Although a lot of the initial media reports of mephedrone-related tragedies were exaggerated or just plain nonsense, there have been a relatively small number of unambiguously mephedrone-caused deaths. If you are sufficiently foolish or unlucky, this stuff can kill you.

But for most people, that isn’t the case. Lots of folks are taking mephedrone, and only a relatively small number have come to grief. Even among those who do crash and burn, most of them get out of it with nothing worse than a very unpleasant night in a hospital emergency room.

But instant death isn’t the only way a drug can mess you up.

A team from University College in London invited local users to pop by the lab on consecutive weekends (once with their drug and once without) so they could get some more objective information about what mephedrone actually does to people.

Alarmingly, they found that even on their drug-free visit, the regular mephedrone users performed substantially worse on a memory test than a comparison group who didn’t take mephedrone.

Although they weren’t mephedrone users, the people in this comparison group did regularly take other drugs, so it isn’t likely – as some critics may have been tempted to surmise – that the mephedrone users were less educated or intelligent than the people they were compared to. Although nobody knows how it’s doing it, it does appear that regular mephedrone use can trash your memory.

More alarming are the findings coming out of Ireland. Mephedrone appears to be particularly damaging when injected, and studies of Irish injecting users report a host of nasty consequences. As one of the study’s participants says:

“It clots up your veins twice as fast as anything else … that’s one thing I did learn fast from it, say you used one vein on it and got two hits out of it, you wouldn’t get the vein again, you’d have to move onto a different vein to get another hit out of it, that’s why everyone started using their groin”.

A case study from a Dublin hospital dealing with the consequences of this contains enough truly gruesome images to convince anyone that recreational mephedrone injecting is not a sensible idea.

Despite that, mephedrone still appears to be on the rise. Reports from Europol and other agencies paint a picture of growing mephedrone consumption across Europe, including injecting use.

They’re also detecting an alarming rise in HIV infections. Mephedrone is particularly nasty as an HIV vector: because users tend to repeatedly re-dose while still intoxicated, safer injecting practices often fall by the wayside. Mephedrone use is also associated with a wide variety of unsafe sexual practices.

Although worldwide use of mephedrone is not yet on the scale seen in Europe, it has penetrated as far as Australia and New Zealand.

From all appearances, mephedrone is not a passing fad. It’s here to stay, and looks likely to add yet another name to the list of problem drugs that prohibition struggles so ineffectually to deal with.